This research project essentially involves an analysis of macrophage differentiation through a study of a series of murine tumor cell lines, which show various degrees of maturation arrest. Many alloantigens and hybridoma-defined cell surface components are becoming available for further definition of subpopulations of cells of macrophage lineages, and these components will be used in a general study of differentiation arrest, intratumor heterogeneity and potential for further induction of differentiation in these cell lines. Particular emphasis is being placed on functional properties (antigen presentation, tumoricidal activity, phagocytosis) and their correlation with cell surface phenotypic markers as defined by monoclonal antibodies at specific differentiation stages.